Design of a Vacuum Chamber for the Magnets of a Separated Sector Cyclotron

The K = 200 separated-sector cyclotron (SSC) of the National Accelerator Centre (NAC) will be used to accelerate both light and heavy ions and requires a vacuum of ~10-5N/m2 for sufficient beam transmission. A vacuum chamber which fits into the narrow (60 mm) pole gap of the sector magnets of this SSC and excludes the pole pieces and the main excitation and field trimming coils from the vacuum has been designed. Factors to be considered in such a design and some design alternatives are discussed. The mechanical design of the thin-walled chamber and of the support structure preventing its collapse is described. An analysis of magnetic field perturbations showed that they can be kept sufficiently small. Necessary precautions and methods to achieve this are presented together with results of the analysis.